It has been known that there are numerous examples of footwear mechanism actuated by means of heel-based pressure, applied when the user steps down. The most common being weight-based pump ventilated footwear. However, this type of footwear is known to be uncomfortable and affects the stability of the footwear because of the vertical heel movement required to actuate the mechanism.
The weight-based pump can be provided in the sole. The sole must be thickened to give room for the pump. This affects the appearance of the footwear.
Thus in the few commercialized designs for weight-based designs, the pump has been made to be quite small thus limiting the negative impacts on stability but also adversely affecting the ventilating abilities of the pump as well.